Arc lamp ignition and operating circuit

ABSTRACT

A circuit for energizing a Xenon arc lamp. A pulse of high potential is applied to the lamp to ionize it and render it conductive. A first capacitor charged to a first voltage less than the high pulse potential discharges current into the lamp after ionization to provide for first stage heating of the electrodes of the lamp. A second capacitor charged to a second potential less than the first and coupled to the lamp through a diode, discharges current into the lamp only after substantial discharge of current from the first capacitor to provide for second stage heating of the electrodes and condition the lamp for continuous conduction. A DC to AC to DC converter is utilized to develop a DC potential which is added to the potential from a battery to provide an operating potential for the continuous operation of the lamp.

United States Patent Strowe Nov. 25, 1975 1 1 ARC LAMP IGNITION AND OPERATING CIRCUIT Inventor:

Primary Examiner-James B. Mullins Attorney, Agent, or Firm-Cooper, Dunham, Clark, Griffin & Moran Robert J. Strowe, Lake Hopatcong, NJ.

[57] ABSTRACT A circuit for energizing a Xenon arc lamp. A pulse of high potential is applied to the lamp to ionize it and [73] Assignee: Streamlight, Inc., King of Prussia,

[22] Filed: Nov. 2, 1973 Appl. No.: 412,123

render it conductive. A first capacitor charged to a first voltage less than the high pulse potential discharges current into the lamp after ionization to provide for first stage heating of the electrodes of the lamp. A second capacitor charged to a second poten- 51 Int.

41/00 tial less than the first and coupled to the lamp through a diode, discharges current into the lamp only after [58] Field of Search......,.......,......,...... 315/173-174,

315/241 R, DIG. 5

substantial discharge of current from the first capacitor to provide for second stage heating of the electrodes and condition the lamp for continuous conduction. A DC to AC to DC converter is utilized to de- S T N m MA 3 E m mT S e 0 RE W N U velop a DC potential which is added to the potential from a battery to provide an operating potential for the continuous operation of the lamp.

6 Claims, 3 Drawing Figures 315/173 X Grimshaw et 315/173 X R 4 2 l 5 3 3,316,445 4/1967 Ahrons........... 3,514,669 5/1970 He1muth.. 3,771,014 11/1973 Paget...........,..... 3,780,342 12/1973 US. Patent Nov. 25, 1975 Sheet 1 of2 3,922,584

I ha. E 15/6/- i L; LAMP OFF a 250 L 1 i g i I LAMP 04/ \1 50" I 15 i I I T/ME Z4 22 J L T I a c, J LAMP SUPPLY HIGH vamzas PULSE sunny,

U.S. Patent Nov. 25, 1975 Sheet 2 on 3,922,584

M A Qw I l 1-- n s m uwww %\\).M Hw fi Q I L 6% s? Q L n l ll llllll l mt W W n N QM r L a Ink NM m NQ k u w a $3 {IL 0 f m uEQQm Q m m FF ARC LAMP IGNITION AND OPERATING CIRCUIT BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION This invention relates to lamp energizing circuits, and more particularly to a circuit for energizing a Xenon arc lamp.

In the past, a high voltage radio frequency source has been employed for initial breakdown of a Xenon arc lamp in conjunction with a source of relatively high voltage for maintaining current flow through the lamp. The disadvantages of such an ignition system are relatively high cost, radio frequency interference during ignition, shortened lamp life because of the adverse effect of the radio frequency discharge, and inefficient lamp operation due to the difference between the open circuit voltage of the power supply and the operating voltage of the lamp during its steady state operation.

The present invention provides for the ignition and operation of an arc lamp, in particular, through use of a circuit that avoids the above disadvantages. Briefly, a DC to AC to DC converter provides a DC potential which is added to that from a DC potential source (for example, a battery) to provide a potential necessary to provide for continuous operation of an arc lamp. Additionally, the DC to AC conversion permits the development of a high potential pulse which is applied to the lamp to ionize it and render it conductive. A continuous (i.e., over a number of cycles) RF. frequency signal is thereby avoided. Additionally, capactive storage is employed of DC potentials (less than the high pulse potential) generated by the converter with successive discharging of plural capacitors into the lamp following the application of the high voltage pulse. Such successive discharging of the capacitors provides for successive stages of heating of the electrodes of the lamp, conditioning the lamp for conduction in a steady state mode. If flashing of the lamp is desired, rather than steady state operation, continuous charging and discharging of the capacitors, in combination with successive applications of high potential pulses is employed along with the removal of the steady state operating potential from the converter.

The following patents are representative of the prior art in this field:

US. Pat. Nos.: 3,697,805 issued Oct. 10, I972 Switsen 3,280,369 issued Oct. I8, I966 Baum et al.

3,l 15,594 issued Dec. 24, I963 Mallory 3,066,243 issued Nov. 27, I962 Mutschler 2,724,792 issued Nov. 22, I955 Nessel 2,575,001 issued Nov. 13, l95l Bird The invention will be more completely understood by reference to the following detailed description, taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a simplified circuit diagram of a lamp ignition and operating circuit in accordance with the invention.

FIG. 2 is a graphical representation of lamp voltage versus time for the circuit of FIG. 1.

FIG. 3 is a detailed schematic circuit diagram of a lamp ignition and operating circuit in accordance with the invention.

DETAILED DESCRIPTION Referring to FIG. I a Xenon arc lamp I0 is shown having electrodes 12 and 14. A circuit for energizing the lamp includes a high voltage pulse supply 16 shown in block diagram form for generating and applying to the lamp a high voltage pulse in the order of 15 to 35 kilovolts, for example. The circuit also includes a first capacitor I8 charged to an initial potential in the order of 250 volts, for example, and a second capacitor 20 charged to an initial potential of about 50 volts, for example. Diodes 22 and 24 are also included, as well as a DC supply 26. These diodes prevent the discharge of the capacitors through the DC supply 26.

In its off state, the potential across the electrodes 12 and 14 of the lamp is equal to the potential across the pre-charged capacitor 18, e.g., 250 volts. This is shown in waveform diagram of FIG. 2 by the time period pre ceding the time t (designated lamp off" in FIG. 2). At the time that the lamp is to be turned on, the high voltage pulse supply I6 generates a high potential pulse, e.g., in the order of 15 to 35 kilovolts. This is shown in FIG. 2 as occurring at time Such a high potential pulse is applied to the electrodes I2 and 14 of the lamp through the capacitor 18 which essentially acts as a bypass during this period of time. Such a high potential applied to the electrodes 12 and I4 of the lamp ionizes the lamp and renders it conductive.

The potential across the electrodes 12 and I4 decays rapidly. This is illustrated in FIG. 2 by the decay of the lamp voltage between the times t and r,. The time scale has been expanded in FIG. 2; the decay is virtually instantaneous. At time t. the potential across the electrodes l2 and I4 of the lamp is equal to the potential across the pre-charged capacitor I8. Following the time t the capacitor l8 discharges slowly through the lamp, which is now conductive. The discharge of current from the capacitor I8 is illustrated by that portion of the curve in FIG. 2 between times I. and During this time period the current discharging through the lamp serves to heat the electrodes of the lamp to provide for first stage heating.

At time I, the potential across the electrodes I2 and I4 of the lamp is equal to the potential across the precharged capacitor 20 (neglecting the potential drop across the diode 22). At this time the capacitor 20 discharges through the lamp, as represented by the time period between times and r: in FIG. 2. The discharge of current from the capacitor 20 provides for second stage heating of the lamp electrodes.

At time t the potential across the electrodes 12 and 14 of the lamp is equal to the potential of the DC supply 26 (neglecting the potential drop across the diodes 22 and 24). The diodes 22 and 24 are thus rendered conductive and the DC supply 26 supplies current to the lamp to render the lamp on". This on' operation of the lamp is designated by lamp on" in FIG. 2 and is represented by the period of time following time It will be noted that the circuit of FIG. I utilizes the two capacitors, pre-charged to different potentials. and coupled to the lamp so that a first one of the capacitors (capacitor 18) discharges current into the lamp, while a second one of the capacitors (capacitor 20) is coupled to the lamp (by diode 22) so that it does not discharge current into the lamp only until after substantial discharge of current from the first capacitor.

A circuit embodying the invention of FIG. 1 is shown in FIG. 3. A DC supply, e.g., a battery (not shown), ap-

pears across conductors 46 and 48. An ON-OFF switch 50 provides for basic on/off control of the overall lamp control circuit. A fan 52 is energized by the DC supply for the purpose of cooling the lamp. Capacitors S4 and 56 are utilized for the purpose of suppressing oscillatrons.

The DC supply is coupled to a multivibrator 58 enclosed by dashed lines in FIG. 3. The multivibrator is conventional in contruction and utilizes a first pair of transistors 60 and 62 connected in Darlington" configuration in which the gain is equal to the gain of one transistor times the gain of the second transistor. A second Darlington configuration of transistors 64 and 66 is employed in the multivibrator. The multivibrator 58 operates with primary winding 72 and feedback winding 68 of the transformer 70. This transformer has a secondary winding 74. The primary winding 72 is coupled to a network consisting of diodes 76, 78, 80 and 82, ganged-together switches 84 and 86, and capacitor 88. This network is utilized for capacitor charging as well as providing an operating potential for the continuous operation of lamp 90, as will be explained in more detail below. The secondary winding 74 is coupled to a network consisting of diodes 92 and 94, capacitors 96, 98 and 100, and resistors 102 and R04 utilized in connection with ignition of the lamp 90 to be explained in more detail below.

In the circuit of FIG. 3, capacitors 100 and 106 correspond respectively to the capacitors l8 and in the circuit of FIG. 1. In other words, these capacitors are successively discharged into the lamp 90, as will be explained in more detail below.

In FIG. 3 diode 108 corresponds to diode 22 in FIG. I. A capacitor 110 shunts the diode I08 tp provide for high voltage (starting pulse) bypassing of the diode.

A high voltage pulse supply 112 is included in the circuit of FIG. 3 corresponding to the supply 16 of FIG. I. This high voltage pulse supply unit includes resistors [14, I16 and 118, capacitor I20, spark gaps 122 and [24, and a transformer 126 having a primary winding 126a and a secondary winding l26b which is connected in series with the lamp 90.

Finally, the circuit of FIG. 3 includes a constant current regulator 128 for the purpose of rendering constant the current flow within the lamp 90. The regulator is conventional and includes transistors 130, 132 and 134, diode 136, and resistors 138, 140, I42 and 114. Of these resistors, the resistor [44 is a ballast resistors having a resistance that is almost negligible, e.g., in the order of 0. IOHM.

To explain the operation of the circuit of FIG. 3, the DC input applied to the conductors 46 and 48 from a battery, for example, is typically in the order of 12 to l4 volts. This supply potential energizes the multivibrator circuitry of windings 68 and 72 of transformer 70. Winding 74 is the high voltage secondary winding of the transformer and typically generates an AC potential of around I000 volts across the entire secondary winding and a potential of about 400 volts across that portion of the secondary winding designated 74a. Diodes 92 and 94 serve as rectifiers, while capacitors 96 and 98 serve as filters. The rectified high voltage potential across the entire secondary winding 74 (as rectified by the diode 92) is applied through resistor 114 to capacitor 120. The capacitor thus stores thereon a charge or rectified high potential. Resistors H6 and I18 serve as voltage dividers to evenly distribute the potential of capacitor 120 across spark gaps 122 and I24, so that one spark gap does not prematurely break down before the other. Charge builds up on capacitor I20 until the voltage across the spark gaps is such as to break them down. Such gaps typically break at about 470 volts, e.g., and then present a relatively low impedance which permits the rapid discharging of capacitor 120 through primary winding 1260. This discharging causes a high voltage pulse to be generated by the secondary winding l26b which is applied to the lamp 90. Such a pulse, in the order of 15 to 35 kilovolts, as described above in connection with the circuit of FIG. I, is utilized to ionize the lamp 90 and to render it conductive.

As noted above, capacitors I00 and I06 correspond to capacitors l8 and 20 in the circuit of FIG. 1 and are utilized for the purposes of electrode heating as will now be explained. The capacitor I00 is charged to a potential of about 200 to 250 volts, e.g., by the action of resistors I02 and 104 which divide the potential across the secondary winding section 74a (this latter potential is in the order of 400 volts, e.g.). After the lamp 90 has been rendered conductive by action of the high voltage pulse supply unit 112 as just described, the capacitor 100 discharges through the lamp to provide for first stage heating of the lamp electrodes. The discharging of the capacitor 100 continues until the potential across the lamp 90 is equal to the potential drop across the storage capacitor 106 (neglecting the potential drop across conductive diode 108). At this time the diode 108 is rendered conductive, permitting this latter capacitor to discharge to provide for second stage heating of the electrodes of the lamp. Capacitor 106 is charged to a potential of from about 35 to 50 volts, e.g., as will now be explained.

The charging of the capacitor 106 is provided for by a voltage "tripling action. In particular, the potential of the source of supply across the conductors 46 and 48 and is added to a part of the potential developed across secondary winding 72. Tracing the current path, conductor 46 is connected through on/off switch 50 by conductor 46a to the center tap 72a of the transformer primary winding 72. The potential developed across the left-hand section of that primary winding is added to the supply potential and is coupled by conductor 88a to capacitor 88. Thus, assuming that the source of supply is l2 volts and that the potential developed across the primary winding half is 12 volts, a total of 24 volts is developed. The capacitor 88 is charged through diode 76 during the conducting period of transistor 60 so that capacitor 88 stores thereon a charge of 12 volts, e.g. During the period when transistor 60 is not conducting and transistor 66 is, the primary winding 72 of transformer connected to wire 88a rises to a potential of 24 volts, e.g. Thus the potential applied to diode 82 is the sum of the voltage of capacitor 88 and the peak voltage of primary winding 72, roughly three times the initial supply potential across the conductors 46 and 48. The diode 82 provides for rectification so that only a DC potential is present at the cathode of the diode for charging the capacitor 106 to the potential mentioned above, e.g., 35 to 50 volts.

The continuous operation of the lamp is provided for by the DC source of supply connected to the conductors 46 and 48 in conjunction with the additional potential generated by the multivibrator 58 including transformer 70 as rectified by diodes 78 and 80. While the source of DC supply may be in the order of l 2 to l4 volts, and the lamp 90 operates continuously at such a voltage, because of the potential drop across the various diodes in the system (for example, diode 108) an additional voltage beyond that supplied by the DC source of supply is needed to run the lamp. The transformer primary winding 72 is connected to diodes 78 and 80 through switches 84 and 86 which are ganged together. These switches are closed when it is desired to operate the lamp 90 continuously. The diodes 78 and 80 provide for full wave rectification of the potential developed across the tapped transformer primary winding 72. The full wave rectified signal is applied through diode 108 to the lamp for the continuous operation of the lamp once it has been ignited. As noted above the constant current regulator I28 serves to regulate the current through the lamp so that it is constant. The transistors 130 and 132 of this constant current regulator control the applied voltage to the multivibrator 58 for this purpose.

As was noted above, the circuit of FIG. 3 is unique in providing for the ignition and operation of lamp 90. By use of the add on" technique by which a potential is developed which is added on to the potential of the DC supply, smaller components can be employed. Thus the multivibrator 58 including transformer 70 can be of less capacity than would be required if these components provided the entire operating potential of the lamp.

If it is desired to operate the lamp 90 in a flasher mode, i.e., the lamp 90 is not operated continuously but rather intermittently, the ganged-together switches 84 and 86 are moved to the open positions. In this configuration the lamp 90 is not supplied with an operating potential needed for continuous operation. The capacitor 120 successively charges and discharges providing for successive high voltage pulses to ionize and render conductive the lamp 90. The capacitors 100 and 106 successively charge and discharge to provide for electrode heating and flashing of the lamp in conjunction with the high voltage pulsing. For a representative circuit configuration as shown in FIG. 3, the flash rate is approximately one flash of the lamp per second.

The invention described above is susceptible of modification. Accordingly, the invention should be taken to be defined by the following claims.

What I claim is:

I. In a circuit for energizing a Xenon arc lamp including means for applying a pulse of high voltage to the lamp to ionize it and render it conductive, the improvement for discharging current into the lamp to heat the electrodes thereof comprising first capacitor means coupled to the lamp and charged to a first voltage less than that of said high voltage for discharging current into said lamp to provide for first stage heating of said electrodes, second capacitor means, charging means for charging said second capacitor means to a second voltage less than said first voltage but substantially higher than the normal operating potential of said lamp for discharging current into said lamp sufficient to provide for second stage heating of said electrodes, and

6 means for coupling said second capacitor means to said lamp for discharging current into said lamp only after substantial discharge of current from said first capacitor means to provide for said second stage heating of said electrodes resulting in enabling the arc lamp to sustain electron conduction.

2. A circuit according to claim 1, including means for supplying an operating potential to said lamp for continuous energization thereof and continuous light output therefrom.

3. A circuit according to claim 1, including means for successively charging said first and second capacitor means which successively discharge into said lamp for providing successive flashes of light output from said lamp.

4. A circuit according to claim 2, including means for removing said operating potential from said lamp and means for successively charging said first and second capacitor means which successively discharge into said lamp for providing successive flashes of light output from said lamp.

5. A circuit for energizing a Xenon arc lamp from a source of DC potential comprising:

a. multivibrator means coupled to said source for developing an AC potential and including transformer means having low potential and high potential winding means,

b. means coupled to said high potential winding means for applying a high potential pulse to said lamp to ionize it and render to conductive,

c. first capacitor means charged by said high potential winding means to a first voltage for discharging current into said lamp to provide for first stage heating of the electrodes of said lamp,

d. second capacitor means charged by said low potential winding means to a second voltage less than said first voltage,

e. coupling means for coupling said second capacitor means to said lamp for discharging current into said lamp only after substantial discharge of current from said first capacitor means to provide for second stage heating of said electrodes resulting in enabling said arc lamp to sustain conduction,

f. rectifying means,

g. said low potential winding means including a section thereof coupled to said source of DC source potential and to said rectifying means for adding said DC source potential to the rectified AC potential generated by said winding section to produce a combined potential which is applied to said lamp for its continuous operation.

6. A circuit according to claim 5 including switch means for inhibiting the application of said combined potential to said lamp to permit the successive flashing of the lamp by successive ones of said high potential pulse and successive charging and discharging of said first and second capacitor means.

a: w a: m 

1. IN A CIRCUIT FOR ENERGIZING A XENON ARC LAMP INCLUDING MEANS FOR APPLYING A PULSE OF HIGH VOLTAGE TO THE LAMP TO IONIZE IT AND RENDER IT CONDUCTIVE, THE IMPROVEMENT FOR DISCHARGING CURRENT INTO THE LAMP TO HEAT THE ELECTRODES THEREOF COMMPRISING FIRST VOLTAGE LESS THAN THAT OF SAID HIGH VOLTAGE FOR CHARGED TO A FIRST VOLTAGE LESS THAN THAT OF SAID HIGH VOLTAGE FO DISCHARGEING CURRENT INTO SAID LAMP TO PROVIDE FOR FIRST STAGE HEATING OF SAID ELECTRODES, SECOND CAPACITOR MEANS, CHARGING MEANS FOR CHARGING SAID SECOND CAPACITOR MAENS TO A SECOND VOLTAGE LESS THAN SAID FIRST VOLTAGE BUT SUBSTANTIALLY HIGHER THA THE NORMAL OPERATING POTENTIAL OF SAID LAMP FOR DISCHARGING CURRENT INTO SAID LAMP SUFFICIENT TO PROVIDE FOR SECOND STAGE HEATING OF SAID ELECTRODES, AND MEANS FOR COUPLING SAI SECOND CAPACITOR MEANS TO SAID LAMP FOR DISCHARGING CURRENT INTO SAI LAMP ONLY AFTER SUBSTANTIAL DISCHARGE OF CURRENT FROM SAID FIRST CAPACITOR MEANS TO PROVIDE FOR SAID SECOND STAGE HEATING OF
 2. A circuit according to claim 1, including means for supplying an operating potential to said lamp for continuous energization thereof and continuous light output therefrom.
 3. A circuit according to claim 1, including means for successively charging said first and second capacitor means which successively discharge into said lamp for providing successive flashes of light output from said lamp.
 4. A circuit according to claim 2, including means for removing said operating potential from said lamp and means for successively charging said first and second capacitor means which successively discharge into said lamp for providing successive flashes of light output from said lamp.
 5. A circuit for energizing a Xenon arc lamp from a source of DC potential comprising: a. multIvibrator means coupled to said source for developing an AC potential and including transformer means having low potential and high potential winding means, b. means coupled to said high potential winding means for applying a high potential pulse to said lamp to ionize it and render to conductive, c. first capacitor means charged by said high potential winding means to a first voltage for discharging current into said lamp to provide for first stage heating of the electrodes of said lamp, d. second capacitor means charged by said low potential winding means to a second voltage less than said first voltage, e. coupling means for coupling said second capacitor means to said lamp for discharging current into said lamp only after substantial discharge of current from said first capacitor means to provide for second stage heating of said electrodes resulting in enabling said arc lamp to sustain conduction, f. rectifying means, g. said low potential winding means including a section thereof coupled to said source of DC source potential and to said rectifying means for adding said DC source potential to the rectified AC potential generated by said winding section to produce a combined potential which is applied to said lamp for its continuous operation.
 6. A circuit according to claim 5 including switch means for inhibiting the application of said combined potential to said lamp to permit the successive flashing of the lamp by successive ones of said high potential pulse and successive charging and discharging of said first and second capacitor means. 